The present invention is directed to a novel method and apparatus for detecting tampering with a dial, such as the dial of a utility meter or the like.
While the invention may find other useful applications, the following description will be facilitated by specific reference to the problem of detecting tampering with a utility meter and particularly with a kilowatt hour meter. Generally speaking, currently manufactured kilowatt hour meters have registers consisting of a plurality of rotary dials having angularly arrayed numerical indicia on their faces and indicators in the form of pointers which are set to rotate on centrally located shafts within each dial or register. Each of these indicators or pointers is mounted to its shaft which is in turn driven by a corresponding gear of a gear train, the gear train being arranged to drive the respective pointers to indicate successive powers of 10 of the kilowatt hours used. Hence, a first dial and pointer indicate the kilowatt hours, a second dial, tens of kilowatt hours, etc.
The pointers of these meters are generally fitted to their shafts only in a friction fit to normally rotate in unison with the shafts. However, the pointers can be manually reset to zero without actually running the gear train to zero, which latter exercise is very time consuming. Accordingly, the utility or other authorized persons can reset all of the pointers to zero manually, for example, when the meter is being prepared for a new service connection.
Unfortunately, many consumers have learned of this feature and have used it to manually move the pointers back in an unauthorized attempt to reduce their apparent energy consumption. While the meters are generally provided with some sort of locking device or other anti-tampering seal to normally prohibit undetected access to the meter dials, consumers often deny knowledge of the source of breakage of such a locking or sealing device. Hence, the utility has no way of determining the existence of tampering or the amount of tampering with the dial with any degree of accuracy. At best, the utility must rely on records of prior usage in an attempt to determine whether there has been tampering and to attempt to arrive at some estimate of the amount of tampering, if any.